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Visible light communication (VLC) has become a promising technology for high data rate communications and an attractive complementary to conventional radio frequency (RF) communication. VLC is a secure, energy efficient and cost-effective technology that exploits the existing infrastructure, particularly in indoor environments, for wireless data transmission. Nevertheless, the main limitation of developing high data rate VLC links is the narrow modulation bandwidth of light-emitting diodes (LEDs), which is in the megahertz range. The power domain nonorthogonal multiple access (PD-NOMA) scheme is envisioned to address several challenges in VLC systems. In this paper, we present a detailed overview of PD-NOMA based VLC systems. Moreover, we introduce insights on some PD-NOMA VLC system constraints and challenges such as power allocation, clipping effect, MIMO and security. Finally, we provide open research problems as well as possible directions for future research to pave the way for the implementation of PD-NOMA VLC systems.

In recent times, nonorthogonal multiple access (NOMA) has appeared as an encouraging system for satisfying the requirements of 5G communications in alleviating the spectrum insufficiency problems. The purpose of NOMA in heterogeneous networks (HetNets) is to increase the spectrum exploitation with the cost of proficient allotment of resources. Therefore, to achieve effective resource assignments for NOMA HetNets, this study develops the best user pairing and efficient power allocation approach. Here, the newly devised optimization method, Feedback Sea Lion Optimization (FSLnO), is employed for achieving a less-difficult optimal solution when user pairing. In addition, the designed FSLnO is also accomplished for performing the energy-efficient power allocation process by enhancing the lesser energy effectiveness of the femtocell users. The Feedback Artificial Tree (FAT) and Sea Lion Optimization (SLnO) are combined to create the developed FSLnO algorithm. Additionally, according to evaluation metrics like achievable rate, energy efficiency, sum rate, and throughput, the developed approach performed better, with maximum values of 2.384 Mbits/s, 0.028 Mbits/Joules, 13.27 5 Mbits/s, and 0.154 Mbps, respectively.

This paper proposes a new framework called pinching antenna systems–nonorthogonal multiple access (PASS–NOMA), which combines the inherent physical properties of waveguide channels with the NOMA technology. The proposed system employs an adaptive pairing strategy with successive interference cancellation to increase the system’s spectral efficiency. The author has utilized the frequency‐selective properties of waveguide channels, including waveguide dispersion, coupling, and propagation of millimeter waves at 30.5 GHz, to increase the efficiency of the proposed system. The simulation results, which use 8 users and 64 subcarriers with a 2.0 GHz bandwidth, have shown that the adaptive PASS–NOMA system achieves 190.6% more throughput compared with traditional OMA schemes with an SNR of 20 dB. It is also shown that the proposed system achieves an average increase of 120.3% across SNR 5–30 dB. The SIC success rates have been found to be 99.8% for an SNR of 30 dB. The fairness index of the proposed system has been found to vary between 0.617 and 0.848, depending on the adaptive pairing strategy. The adaptive system offers a reasonable trade‐off between throughput and fairness. The proposed system achieves near‐perfect fairness of 0.848 with the random pairing strategy, and the overall system performance is robust. The simulation results have confirmed the potential of waveguide‐aware NOMA architectures for 6G indoor networks, which require high spectral efficiency and reliable multiuser connectivity.

The massive connectivity requirement and security issues have become major factors restricting the further development of the Internet of Things. Nonorthogonal multiple access (NOMA) can be combined with physical layer security (PLS) to achieve massive connectivity and secure transmission. This article investigates the PLS performance for a downlink communication system over Nakagami-m fading channels, with full-duplex (FD) cooperative NOMA transmission aided by artificial noise (AN). While direct communication is built between the base station and two NOMA users, the strong user is employed as an FD relay as well as the jammer to enhance the PLS of the legitimate transmission in the presence of a passive eavesdropper (Eve). Closed-form analytical expressions in terms of the outage probability of the legitimate users and the intercept probability of Eve are derived to evaluate the security–reliability trade-off (SRT) of the proposed scheme. Monte Carlo simulations are provided to validate the veracity of the theoretic analyses and illustrate that the proposed scheme is superior in terms of SRT to the benchmark schemes in the low SNR region. Furthermore, the results reveal that the SRT performance of the two NOMA users can be enhanced through a proper AN-bearing ratio and power allocation optimization.

Generalized Singular Value Decomposition (GSVD) is the enabling linear precoding scheme for multiple-input multiple-output (MIMO) non-orthogonal multiple access (NOMA) systems. In this paper, we extend research concerning downlink MIMO-NOMA systems with GSVD to cover bit error rate (BER) performance and to derive an approximate evaluation of the average BER performance. Specifically, we deploy, at the base station, the well-known technique of joint-modulation to generate NOMA symbols and joint maximum-likelihood (ML) to recover the transmitted data at end user locations. Consequently, the joint ML detector offers almost the same performance, in terms of average BER as ideal successive interference cancellation. Next, we also investigate BER performance of other precoding schemes, such as zero-forcing, block diagonalization, and simultaneous triangularization, comparing them with GSVD. Furthermore, BER performance is verified in different configurations in relation to the number of antennas. In cases where the number of transmit antennas is greater than twice the number of receive antennas, average BER performance is superior.

The number of wireless devices, as well as their traffic volumes, is constantly growing, which degrades the quality of service. To combat this problem, the new Wi-Fi 6 (IEEE 802.11ax) standard introduces the orthogonal frequency division multiple access (OFDMA) mechanism, which allows coordinated multiuser frequency division transmissions. In addition, there is another user multiplexing mechanism, non-orthogonal multiple access (NOMA), that allows transmitting on the same frequencies simultaneously and separating different signals by power level. This paper considers the joint usage of these mechanisms for uplink transmissions in Wi-Fi 6 networks and sets the problem of optimal radio resource allocation between the users to maximize some utility functions, for example, the geometric mean throughput. To solve it, we propose an algorithm that takes into account the channel frequency selectivity and uses OFMDA and NOMA simultaneously. It is shown that the joint usage of OFDMA and NOMA can significantly increase the network throughput and reduce delays.

Abstract—The problem of uplink multiplexing of two different types of traffic specific to 5G networks (enhanced Mobile Broadband traffic (eMBB) and Ultra-Reliable Low-Latency Communications (URLLC)) is considered. A dynamic multiplexing scheme based on the use of the nonorthogonal multiple access is proposed. An analytical model is developed to estimate the network performance using the proposed scheme, as well as to select its optimal parameters in order to maximize the network capacity for eMBB traffic while fulfilling the quality of service requirements for URLLC traffic.

As an important port technology in mobile communication, multiple access can effectively improve the number of user access in the communication system. However, the Orthogonal Multiple Access (OMA) technology has been unable to meet the higher requirements of spectrum efficiency and system capacity in the future, so it is of great practical significance to study and design a new multiple access technology. Sparse Code Multiple Access (SCMA), as a new non-orthogonal multiple Access (NOMA) scheme, improves the number of user access and spectrum utilization by superposition of multi-user information on the same time-frequency resource. And it can well adapt to all kinds of new application scenarios in 5G. This paper introduces SCMA technology from four aspects: basic principle, system model, key technology and its combination with other systems.

Space-division multiple access (SDMA) utilizes linear precoding to separate users in the spatial domain and relies on fully treating any residual multi-user interference as noise. Non-orthogonal multiple access (NOMA) uses linearly precoded superposition coding with successive interference cancellation (SIC) to superpose users in the power domain and relies on user grouping and ordering to enforce some users to fully decode and cancel interference created by other users.In this paper, we argue that to efficiently cope with the high throughput, heterogeneity of quality of service (QoS), and massive connectivity requirements of future multi-antenna wireless networks, multiple access design needs to depart from those two extreme interference management strategies, namely fully treat interference as noise (as in SDMA) and fully decode interference (as in NOMA).Considering a multiple-input single-output broadcast channel, we develop a novel multiple access framework, called rate-splitting multiple access (RSMA). RSMA is a more general and more powerful multiple access for downlink multi-antenna systems that contains SDMA and NOMA as special cases. RSMA relies on linearly precoded rate-splitting with SIC to decode part of the interference and treat the remaining part of the interference as noise. This capability of RSMA to partially decode interference and partially treat interference as noise enables to softly bridge the two extremes of fully decoding interference and treating interference as noise and provides room for rate and QoS enhancements and complexity reduction.The three multiple access schemes are compared, and extensive numerical results show that RSMA provides a smooth transition between SDMA and NOMA and outperforms them both in a wide range of network loads (underloaded and overloaded regimes) and user deployments (with a diversity of channel directions, channel strengths, and qualities of channel state information at the transmitter). Moreover, RSMA provides rate and QoS enhancements over NOMA at a lower computational complexity for the transmit scheduler and the receivers (number of SIC layers).

Today’s wireless networks allocate radio resources to users based on the orthogonal multiple access (OMA) principle. However, as the number of users increases, OMA based approaches may not meet the stringent emerging requirements including very high spectral efficiency, very low latency, and massive device connectivity. Nonorthogonal multiple access (NOMA) principle emerges as a solution to improve the spectral efficiency while allowing some degree of multiple access interference at receivers. In this tutorial style paper, we target providing a unified model for NOMA, including uplink and downlink transmissions, along with the extensions to multiple input multiple output and cooperative communication scenarios. Through numerical examples, we compare the performances of OMA and NOMA networks. Implementation aspects and open issues are also detailed.